Rossum will play Ridley, a cousin who becomes a dark witch and becomes an enemy to the protagonist.
The film is based off the young adult fantasy book by Kami Garcia and Margaret Stohl of the â€œBeautiful Creaturesâ€ series.
The plotline follows the character Lena Duchannes hiding her powers from the Southern town of Gatlin and her relationship with a local boy Ethan Wate.
Other cast members already included Jack Oâ€™Connell, Alice Englert, Viola Davis and Emma Thompson.
The film has a 2013 realease date with a production start date next month.
Rossum currently stars in the Showtimeâ€™s television series â€œShamelessâ€ with William H. Macy. Her past film credits included â€œThe Day After Tomorrow,â€ â€œThe Phantom of the Opera,â€ â€œMystic Riverâ€ and â€œPoseidon.â€